The present disclosure relates to an image sensor and a fabrication method thereof.
Image sensors are semiconductor devices that convert an optical image into an electrical signal. The image sensors are generally classified into a charge-coupled device (CCD) image sensor and a complementary metal-oxide-semiconductor (CMOS) image sensor.
The CMOS image sensor typically includes a photodiode region converting a received optical signal into an electrical signal, and a transistor region processing the electrical signal, wherein the photodiode region and the transistor region are disposed horizontally.
In such a horizontal image sensor, a photodiode region and a transistor region are disposed horizontally on a semiconductor substrate. Therefore, the horizontal image sensor has a limitation in expanding an optical sensing region in a limited area, which is generally referred to as a fill factor.